Radiant underslab insulation question

Myron

I hadn't heard of InsulTarp before, and looking at the info I have been able to find on the web it looks like the ideal product for this application.

As far as the 24" on center, I will only heat the barn to about 55 degrees, and it is primarily storage of equipment, etc, not a working area. According to my calculations I can easily heat it with only 85 degree water and the heatloss is only about 15 btu/sq foot.

Is there another reason I should put the tubing closer together? There will be a small office in one corner, and this tube will be on standard 12" centers.

Myron

Radiant underslab insulation question

I am building a barn, that will have be heated radiantly with 24" on-center tubing. I was planning on installing
styrofoam as an under slab insulation, but my concrete contractor is telling me that I should use something like radiant foil. He thinks this is better because it doesn't break/crack like styrofoam will, but again, I am concerned
that this won't be very effective. His concern seems to be with the fact that stryofoam will break as they walk on it, which he seems to think will greatly reduce its effectiveness.

The general idea is that the bubble insulation has vinyl on one side, so that the calcium in the concrete won't react with it, and the shiny side goes down against the ground.

I am concerned that there obviously won't be an air gap, but the people that sell the stuff say you don't need one in this application. (They aren't able to tell me why it isn't needed, although they agree that an air gap is needed in the walls and ceilings). One guy claimed that 5/16" bubble and foil is more effective than 1" of styrofoam, which I find really hard to believe.

The argument seems to be that foam works because of mass, and that it will eventually get warm all the way through, i.e. saturated with heat, at which point it supposedly loses something. But common sense would tell me that it would be much, much warmer under a thin bubble foil layer than under 1" of styrofoam although I may be wrong. I find it hard to believe that more is gained by reflecting infrared rays back up into the concrete that would otherwise be lost into the soil, then is lost by conduction into the ground through a relatively thin layer of insulation. Furthermore, I think it is questionable how much reflectivity is even possible by having the foil just under the concrete with the shiny side down.

I thought about using a combination of foam and foil, but this seems rather cost prohibitive for what may essentially be very little gain. One guy thought the foil should go under the foam and then later changed his mind that it might be better on top, just under the concrete. I get the
feeling that the sale is most important, not whether it works for my application.

One web site even claims that the air gap only needs to be the thickness of a thumbnail to work effectively, but this flys in the face of every scientific study I have ever read regarding the requirement for an adequate air gap.

Anyway, this is one area I don't want to screw up on, as it will be impossible to fix after the concrete is poured. Your expert opinions in this matter would be greatly appreciated.

hot_rod

Hard telling

You concrete guy brings up excellent points. Unless the subgrade is very smooth and level, with small aggreate, plan on seeing some broken pieces of 1" foamboard!

The tarp and roll products are much better in this regard, and do offer a better vapor barrier. I still question the actual R-value of the various foil/ bubble products. It's the air space that make up the R-number. The bubble manufactures count on reflectivity as part of the equasion. I noticed most manufactiures now call it "radiant barrier" not insulation.

Other concerns center around the long lastingness of those "bubbles" Will the break down? How much will that effect the insulation value? How will we know?

Currently there are no official standards to test these products to, for this application,so claims vary, a bit.

My current method is to use 1-1/2" foam for my edge insulation, and at least a 2 foot wide perimeter band. Then I switch to the InsulTarp for the interior portions.

Keep in mind foamboard has it's drawbacks also. In addition to it breaking easily, insect resistence is the main short coming. Years ago the EPA banned the chemical used for termite protection. If this is a concen in your area, consider having the area treated before the board is put down. Insects will consume, and nest in the warm foam, given an opportunity!

There are still some foam manufactures treating with borates, for insect resistence. It is not a long lasting protection however, like the previously used, possibly toxic, cloradanes (sp)

hot rod

Dave H_2

If You are concerned

about the cracking of the styrofoam, don't use it.

For a stronger material, use extruded polystyrene. You can get this in different compressive strengths and is much stronger than the white styrofoam.

Also, so what if it cracks, the insulative value will still be there.

Good Luck

steve gates

I won't

debate foam vs. foil but I say with foam and cracking it's how well you prepare the soil underneath. Hard and flat. I hope the concrete guy isn't setting up for excuses why it cracks and it's because of radiant.

I'd wouln'd do 24" centers no matter what size the tubing is either.

bruce pirger

Hi Myron, I'm not a radiant installer or anything, but I did install it in my new house. I put 2" of the expanded polystyrene under the entire floor...you can only do it once I figure...and I laid it on top of a smooth (and compacted) layer of #1 stone...small stuff. I don't think we broke any of the 2x8 sheets I laid down during the pour.

My day job has me do astronomy/engineering. I can't believe for a moment that those radiant bubble wraps are anywhere near as good for underslab use. The heat transfer to the ground will be so dominated by conduction....I can't believe they'd come close.

I did not know about the Insultarp product...

And the polystyrene, and all insulation, will develop a thermal gradiant within the material. Hot on the floor side, cool on the ground sound. Heat will flow through the insulation based on the temperature difference (the higher the difference the higher the flow) and also based on the paramaters of the insulation. Everything works this way, as far as insulation goes. Wood is the same...a graident across your plywood or 2x6 stud works the same. The temperature difference is the same (inside-outside), but the material properties are very different.

Now I haven't done any detailed analysis...but I find it hard to accept the foil bubble wrap does much. Seems to me like lots of folks are making lots of money...but I don't know. I would be very interested in seeing a test.

In radiat applications, were there low emissivity foil paper can make a difference, ie places with an air space, I can accept the benefits of the material. But under a slab were conduction is dominant...I think you are right on the money.

Put some heat in my slab for the first time on Monday as it was cool (55) outside and miserable all day (perpetual rain) and WOW, it was so sweet to walk around barefoot! YAHOO! Been waiting for it to get COLD...can't wait.

Radiant Wizard

R-Foil

Radiant Wizard

R-Foil

Watch out there are alot of bad bubble wrap products out there. The only one that I know of and have used that has a lifetime warranty for your exact application is R-Foil by Cover-Tech.

Rock Solid Restoration_3

What exactly do they warranty?

Rock Solid Restoration_3

Super Tuff R

Myron

I've done some radiant in my basement and in my garage, I use 2" thick Super Tuff R. It is Foil Faced Polyisocyanurate. It has a higher R- Value per inch than the Extruded Polystyrene, and it has the benefit of the foil face to reflect the radiant heat. It costs about the same as the polystyrene. I haven't cracked a piece yet.

Rock Solid Restoration_3

Myron

I've installed radiant in my basement and my garage.

I use 2" of foil faced polyisocyanurate. It is called Super Tuff R. It can be purchased at Home Depot. It has a higher R-value than the extruded polystyrene and has the added benefit of the foil face to reflect the radiant. I haven't cracked a piece yet.

If you go that route, a word of caution, if your subgrade is not very flat, the insulation may span small depressions in the subgrade during the pour. This will leave a void between the bottom of your slab and your subgrade after the concrete cures. Then, if you bring something heavy onto that area, you are asking the slab to span that void and it could crack. Avoid this problem by doing a good job of leveling and compacting your subgrade. And by using wire mesh in the bottom 1/3 of your slab.

Also,don't forget your 6mil Poly vapor barrier first.

I don't know how big your barn is, but if it were me, I would cough up the extra dough and put my tubing closer together. Wouldn't it be a shame if down the road one day you did want to use that space to work on something rather than just storage and you wanted it to be warmer, then what.

Good luck

Craig

Boilerpro_3

Polyisocyanurate aging

Just remember isocyanurate off gasses and at the end of 20 to 25 years all you have is the standard R-5 per inch not R-7.5 per inch. I'd design for R-5 per inch.

Boilerpro

Rock Solid Restoration_3

Thanks for the info, I didn't know that.

What exactly is it off-gassing. Is it dangerous to use in an interior application?

kevin_5

Foil side up?

Hey Myron, I have heard that the concrete will wreck the foil face pretty soon, leaving you with the foam. (which of course is still more than many people have anyway) Have you heard anything like that? Then again, it seems to be an question of whether the foil would have done anything anyway. I personally like the Low E brand foam/foil/foam as opposed to the foil bubble. I think it would have more resistance to "going flat." Enjoy your garage! Kevin

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MMC

subgradesystem

clean compacted fill,10mil vapor barrier,2"blue board insulation,3-4"clean compacted fill(this will hold vapor&insulation in place&give soil under the concrete allowing the water in the concrete to hydrate into it) next step place your wire mesh sheets&tubing(tubing@12"oc +-),now pour your floor.remember insulation is cheap compared to energy,tubing is also cheap,more tubing mean lower water tempatures.the costs of heating systems is not the initial costs but the long term operating costs,the cost of energy is the one cost that will not go down.

Boilerpro_3

Don't remember exactly on both

but I don't remember reading any particular dangers. The material that off gasses, if mermory serves, is the gas pumped into the foam to displace normal air. The gas used is much less thermally conductive than air, so it improves the R-value (ie. Argon filled thermopanes vs. standard thermopanes). Since the off gasssing is so slow, I imagine it does not have time to build up. Also, under a slab and above the vapor barrier, off gassing may be further slowed.
I'd call the manufacturer on this and ask for info on aged R-values.

Boilerpro

Myron

Thanks!

Thanks for all the info, which I found very interesting. My barn is 40'x60', and there will be a 20'x20' office area in one corner that is at 1' on center. But according to Wirsbo's software I don't gain much reduction in water temp by installing the tubing at 1' on center in the main area, even when the setpoint is raised from 55 deg to 65 deg. It does add considerable cost in piping and labor, so I don't see the justification of installing it closer than 2' on center.

Sure, it would make it more comfortable if I were walking on it without shoes, but I seriously doubt that I will be doing this. And it would probably dry a more evenly when wet, but either way is much better than a unit heater hanging at the ceiling! About 6 or 7 years ago I installed another workshop type projects with this spacing without any complaints, and this was at a retirement community where old men go to putter away the day. And if they didn't notice the difference, I don't think I will either.

But I will be glad to listen if someone has a another good reason why the tubing should be closer. It seems to me that as long as I can get the BTUs I need, either way should work fine.

Myron

Thanks!

Thanks for all the info, which I found very interesting. My barn is 40'x60', and there will be a 20'x20' office area in one corner that is at 1' on center. But according to Wirsbo's software I don't gain much reduction in water temp by installing the tubing at 1' on center in the main area, even when the setpoint is raised from 55 deg to 65 deg. It does add considerable cost in piping and labor, so I don't see the justification of installing it closer than 2' on center.

Sure, it would make it more comfortable if I were walking on it without shoes, but I seriously doubt that I will be doing this. And it would probably dry a more evenly when wet, but either way is much better than a unit heater hanging at the ceiling! About 6 or 7 years ago I installed another workshop type projects with this spacing without any complaints, and this was at a retirement community where old men go to putter away the day. And if they didn't notice the difference, I don't think I will either.

But I will be glad to listen if someone has a another good reason why the tubing should be closer. It seems to me that as long as I can get the BTUs I need, either way should work fine.